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<tr class="t-nv-h1"><td colspan="5"> 函数</td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="feclearexcept.html" title="c/numeric/fenv/feclearexcept"><span class="t-lines"><span>feclearexcept</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-c99">(C99)</span></span></span></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="fetestexcept.html" title="c/numeric/fenv/fetestexcept"><span class="t-lines"><span>fetestexcept</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-c99">(C99)</span></span></span></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="feraiseexcept.html" title="c/numeric/fenv/feraiseexcept"><span class="t-lines"><span>feraiseexcept</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-c99">(C99)</span></span></span></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="feexceptflag.html" title="c/numeric/fenv/feexceptflag"><span class="t-lines"><span>fegetexceptflag</span><span>fesetexceptflag</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-c99">(C99)</span></span><span><span class="t-mark-rev t-since-c99">(C99)</span></span></span></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="feround.html" title="c/numeric/fenv/feround"><span class="t-lines"><span>fegetround</span><span>fesetround</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-c99">(C99)</span></span><span><span class="t-mark-rev t-since-c99">(C99)</span></span></span></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><strong class="selflink"><span class="t-lines"><span>fegetenv</span><span>fesetenv</span></span></strong></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-c99">(C99)</span></span></span></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="feholdexcept.html" title="c/numeric/fenv/feholdexcept"><span class="t-lines"><span>feholdexcept</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-c99">(C99)</span></span></span></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="feupdateenv.html" title="c/numeric/fenv/feupdateenv"><span class="t-lines"><span>feupdateenv</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-c99">(C99)</span></span></span></div></div></td></tr>
<tr class="t-nv-h1"><td colspan="5"> 宏常量</td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="FE_exceptions.html" title="c/numeric/fenv/FE exceptions"><span class="t-lines"><span>FE_ALL_EXCEPT</span><span>FE_DIVBYZERO</span><span>FE_INEXACT</span><span>FE_INVALID</span><span>FE_OVERFLOW</span><span>FE_UNDERFLOW</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-c99">(C99)</span></span></span></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="FE_round.html" title="c/numeric/fenv/FE round"><span class="t-lines"><span>FE_DOWNWARD</span><span>FE_TONEAREST</span><span>FE_TOWARDZERO</span><span>FE_UPWARD</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-c99">(C99)</span></span></span></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="FE_DFL_ENV.html" title="c/numeric/fenv/FE DFL ENV"><span class="t-lines"><span>FE_DFL_ENV</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-c99">(C99)</span></span></span></div></div></td></tr>
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<table class="t-dcl-begin"><tbody>
<tr class="t-dsc-header">
<td> <div>定义于头文件 <code>&lt;fenv.h&gt;</code>
 </div></td>
<td></td>
<td></td>
</tr>
<tr class="t-dcl t-since-c99">
<td> <div><span class="mw-geshi c source-c"><span class="kw4">int</span> fegetenv<span class="br0">(</span> fenv_t<span class="sy2">*</span> envp <span class="br0">)</span><span class="sy4">;</span></span></div></td>
<td> (1) </td>
<td> <span class="t-mark-rev t-since-c99">(C99 起)</span> </td>
</tr>
<tr class="t-dcl t-since-c99">
<td> <div><span class="mw-geshi c source-c"><span class="kw4">int</span> fesetenv<span class="br0">(</span> <span class="kw4">const</span> fenv_t<span class="sy2">*</span> envp <span class="br0">)</span><span class="sy4">;</span></span></div></td>
<td> (2) </td>
<td> <span class="t-mark-rev t-since-c99">(C99 起)</span> </td>
</tr>
<tr class="t-dcl-sep"><td></td><td></td><td></td></tr>
</tbody></table>
<p>1) 试图存储浮点环境的状态于 <code>envp</code> 所指向的对象。
</p><p>2) 试图从 <code>envp</code> 所指向的对象建立浮点环境状态。对象的值必须是以先前调用 <span class="t-lc"><a href="feholdexcept.html" title="c/numeric/fenv/feholdexcept">feholdexcept</a></span> 或 <code>fegetenv</code> 获得值或是浮点宏常量。若 <code>envp</code> 中设置了任何浮点状态标志，则环境中标志变为被设置（然后可用 <span class="t-lc"><a href="fetestexcept.html" title="c/numeric/fenv/fetestexcept">fetestexcept</a></span> 测试），但不引发对应的浮点异常（执行持续而不中断）。
</p>
<h3><span class="mw-headline" id=".E5.8F.82.E6.95.B0">参数</span></h3>
<table class="t-par-begin">


<tr class="t-par">
<td>  envp
</td>
<td> -
</td>
<td> 指向 <span class="t-c"><span class="mw-geshi c source-c">fenv_t</span></span> 类型对象的指针，该对象保有浮点环境的状态
</td></tr></table>
<h3><span class="mw-headline" id=".E8.BF.94.E5.9B.9E.E5.80.BC">返回值</span></h3>
<p>成功时返回 <span class="t-c"><span class="mw-geshi c source-c">​<span class="nu0">0</span>​</span></span> ，否则返回非零。
</p>
<h3><span class="mw-headline" id=".E7.A4.BA.E4.BE.8B">示例</span></h3>
<div class="t-example"><div class="t-example-live-link"><div class="coliru-btn coliru-btn-run-init">运行此代码</div></div>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="c source-c"><pre class="de1"><span class="co2">#include &lt;stdio.h&gt;</span>
<span class="co2">#include &lt;math.h&gt;</span>
<span class="co2">#include &lt;fenv.h&gt;</span>
 
<span class="co2">#pragma STDC FENV_ACCESS ON</span>
 
<span class="kw4">void</span> show_fe_exceptions<span class="br0">(</span><span class="kw4">void</span><span class="br0">)</span>
<span class="br0">{</span>
    <a href="../../io/fprintf.html"><span class="kw849">printf</span></a><span class="br0">(</span><span class="st0">"current exceptions raised: "</span><span class="br0">)</span><span class="sy4">;</span>
    <span class="kw1">if</span><span class="br0">(</span><a href="fetestexcept.html"><span class="kw719">fetestexcept</span></a><span class="br0">(</span><a href="FE_exceptions.html"><span class="kw728">FE_DIVBYZERO</span></a><span class="br0">)</span><span class="br0">)</span>     <a href="../../io/fprintf.html"><span class="kw849">printf</span></a><span class="br0">(</span><span class="st0">" FE_DIVBYZERO"</span><span class="br0">)</span><span class="sy4">;</span>
    <span class="kw1">if</span><span class="br0">(</span><a href="fetestexcept.html"><span class="kw719">fetestexcept</span></a><span class="br0">(</span><a href="FE_exceptions.html"><span class="kw729">FE_INEXACT</span></a><span class="br0">)</span><span class="br0">)</span>       <a href="../../io/fprintf.html"><span class="kw849">printf</span></a><span class="br0">(</span><span class="st0">" FE_INEXACT"</span><span class="br0">)</span><span class="sy4">;</span>
    <span class="kw1">if</span><span class="br0">(</span><a href="fetestexcept.html"><span class="kw719">fetestexcept</span></a><span class="br0">(</span><a href="FE_exceptions.html"><span class="kw730">FE_INVALID</span></a><span class="br0">)</span><span class="br0">)</span>       <a href="../../io/fprintf.html"><span class="kw849">printf</span></a><span class="br0">(</span><span class="st0">" FE_INVALID"</span><span class="br0">)</span><span class="sy4">;</span>
    <span class="kw1">if</span><span class="br0">(</span><a href="fetestexcept.html"><span class="kw719">fetestexcept</span></a><span class="br0">(</span><a href="FE_exceptions.html"><span class="kw731">FE_OVERFLOW</span></a><span class="br0">)</span><span class="br0">)</span>      <a href="../../io/fprintf.html"><span class="kw849">printf</span></a><span class="br0">(</span><span class="st0">" FE_OVERFLOW"</span><span class="br0">)</span><span class="sy4">;</span>
    <span class="kw1">if</span><span class="br0">(</span><a href="fetestexcept.html"><span class="kw719">fetestexcept</span></a><span class="br0">(</span><a href="FE_exceptions.html"><span class="kw732">FE_UNDERFLOW</span></a><span class="br0">)</span><span class="br0">)</span>     <a href="../../io/fprintf.html"><span class="kw849">printf</span></a><span class="br0">(</span><span class="st0">" FE_UNDERFLOW"</span><span class="br0">)</span><span class="sy4">;</span>
    <span class="kw1">if</span><span class="br0">(</span><a href="fetestexcept.html"><span class="kw719">fetestexcept</span></a><span class="br0">(</span><a href="FE_exceptions.html"><span class="kw727">FE_ALL_EXCEPT</span></a><span class="br0">)</span><span class="sy1">==</span><span class="nu0">0</span><span class="br0">)</span> <a href="../../io/fprintf.html"><span class="kw849">printf</span></a><span class="br0">(</span><span class="st0">" none"</span><span class="br0">)</span><span class="sy4">;</span>
    <a href="../../io/fprintf.html"><span class="kw849">printf</span></a><span class="br0">(</span><span class="st0">"<span class="es1">\n</span>"</span><span class="br0">)</span><span class="sy4">;</span>
<span class="br0">}</span>
 
<span class="kw4">void</span> show_fe_rounding_method<span class="br0">(</span><span class="kw4">void</span><span class="br0">)</span>
<span class="br0">{</span>
    <a href="../../io/fprintf.html"><span class="kw849">printf</span></a><span class="br0">(</span><span class="st0">"current rounding method:    "</span><span class="br0">)</span><span class="sy4">;</span>
    <span class="kw1">switch</span> <span class="br0">(</span><a href="feround.html"><span class="kw723">fegetround</span></a><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span> <span class="br0">{</span>
           <span class="kw1">case</span> <a href="FE_round.html"><span class="kw734">FE_TONEAREST</span></a><span class="sy4">:</span>  <a href="../../io/fprintf.html"><span class="kw849">printf</span></a> <span class="br0">(</span><span class="st0">"FE_TONEAREST"</span><span class="br0">)</span><span class="sy4">;</span>  <span class="kw1">break</span><span class="sy4">;</span>
           <span class="kw1">case</span> <a href="FE_round.html"><span class="kw733">FE_DOWNWARD</span></a><span class="sy4">:</span>   <a href="../../io/fprintf.html"><span class="kw849">printf</span></a> <span class="br0">(</span><span class="st0">"FE_DOWNWARD"</span><span class="br0">)</span><span class="sy4">;</span>   <span class="kw1">break</span><span class="sy4">;</span>
           <span class="kw1">case</span> <a href="FE_round.html"><span class="kw736">FE_UPWARD</span></a><span class="sy4">:</span>     <a href="../../io/fprintf.html"><span class="kw849">printf</span></a> <span class="br0">(</span><span class="st0">"FE_UPWARD"</span><span class="br0">)</span><span class="sy4">;</span>     <span class="kw1">break</span><span class="sy4">;</span>
           <span class="kw1">case</span> <a href="FE_round.html"><span class="kw735">FE_TOWARDZERO</span></a><span class="sy4">:</span> <a href="../../io/fprintf.html"><span class="kw849">printf</span></a> <span class="br0">(</span><span class="st0">"FE_TOWARDZERO"</span><span class="br0">)</span><span class="sy4">;</span> <span class="kw1">break</span><span class="sy4">;</span>
           <span class="kw1">default</span><span class="sy4">:</span>            <a href="../../io/fprintf.html"><span class="kw849">printf</span></a> <span class="br0">(</span><span class="st0">"unknown"</span><span class="br0">)</span><span class="sy4">;</span>
    <span class="br0">}</span><span class="sy4">;</span>
    <a href="../../io/fprintf.html"><span class="kw849">printf</span></a><span class="br0">(</span><span class="st0">"<span class="es1">\n</span>"</span><span class="br0">)</span><span class="sy4">;</span>
<span class="br0">}</span>
 
<span class="kw4">void</span> show_fe_environment<span class="br0">(</span><span class="kw4">void</span><span class="br0">)</span>
<span class="br0">{</span>
    show_fe_exceptions<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
    show_fe_rounding_method<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
<span class="br0">}</span>    
 
<span class="kw4">int</span> main<span class="br0">(</span><span class="kw4">void</span><span class="br0">)</span>
<span class="br0">{</span>
    fenv_t curr_env<span class="sy4">;</span>
    <span class="kw4">int</span> rtn<span class="sy4">;</span>
 
    <span class="coMULTI">/* 显示默认环境。 */</span>
    show_fe_environment<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
    <a href="../../io/fprintf.html"><span class="kw849">printf</span></a><span class="br0">(</span><span class="st0">"<span class="es1">\n</span>"</span><span class="br0">)</span><span class="sy4">;</span>
 
    <span class="coMULTI">/* 在默认环境下做一些计算。 */</span>
    <a href="../../io/fprintf.html"><span class="kw849">printf</span></a><span class="br0">(</span><span class="st0">"+11.5 -&gt; %+4.1f<span class="es1">\n</span>"</span>, <a href="../math/rint.html"><span class="kw693">rint</span></a><span class="br0">(</span><span class="sy2">+</span><span class="nu16">11.5</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span> <span class="coMULTI">/* 两整数的中央值 */</span>
    <a href="../../io/fprintf.html"><span class="kw849">printf</span></a><span class="br0">(</span><span class="st0">"+12.5 -&gt; %+4.1f<span class="es1">\n</span>"</span>, <a href="../math/rint.html"><span class="kw693">rint</span></a><span class="br0">(</span><span class="sy2">+</span><span class="nu16">12.5</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span> <span class="coMULTI">/* 两整数的中央值 */</span>
    show_fe_environment<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
    <a href="../../io/fprintf.html"><span class="kw849">printf</span></a><span class="br0">(</span><span class="st0">"<span class="es1">\n</span>"</span><span class="br0">)</span><span class="sy4">;</span>
 
    <span class="coMULTI">/* 保存当前环境。 */</span>
    rtn <span class="sy1">=</span> fegetenv<span class="br0">(</span><span class="sy3">&amp;</span>curr_env<span class="br0">)</span><span class="sy4">;</span>
 
    <span class="coMULTI">/* 以新舍入方法进行一些计算。 */</span>
    <a href="feclearexcept.html"><span class="kw718">feclearexcept</span></a><span class="br0">(</span><a href="FE_exceptions.html"><span class="kw727">FE_ALL_EXCEPT</span></a><span class="br0">)</span><span class="sy4">;</span>
    <a href="feround.html"><span class="kw724">fesetround</span></a><span class="br0">(</span><a href="FE_round.html"><span class="kw733">FE_DOWNWARD</span></a><span class="br0">)</span><span class="sy4">;</span>
    <a href="../../io/fprintf.html"><span class="kw849">printf</span></a><span class="br0">(</span><span class="st0">"1.0/0.0 = %f<span class="es1">\n</span>"</span>, <span class="nu16">1.0</span><span class="sy2">/</span><span class="nu16">0.0</span><span class="br0">)</span><span class="sy4">;</span>
    <a href="../../io/fprintf.html"><span class="kw849">printf</span></a><span class="br0">(</span><span class="st0">"+11.5 -&gt; %+4.1f<span class="es1">\n</span>"</span>, <a href="../math/rint.html"><span class="kw693">rint</span></a><span class="br0">(</span><span class="sy2">+</span><span class="nu16">11.5</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
    <a href="../../io/fprintf.html"><span class="kw849">printf</span></a><span class="br0">(</span><span class="st0">"+12.5 -&gt; %+4.1f<span class="es1">\n</span>"</span>, <a href="../math/rint.html"><span class="kw693">rint</span></a><span class="br0">(</span><span class="sy2">+</span><span class="nu16">12.5</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
    show_fe_environment<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
    <a href="../../io/fprintf.html"><span class="kw849">printf</span></a><span class="br0">(</span><span class="st0">"<span class="es1">\n</span>"</span><span class="br0">)</span><span class="sy4">;</span>
 
    <span class="coMULTI">/* 恢复先前环境。 */</span>
    rtn <span class="sy1">=</span> fesetenv<span class="br0">(</span><span class="sy3">&amp;</span>curr_env<span class="br0">)</span><span class="sy4">;</span>
    show_fe_environment<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
 
    <span class="kw1">return</span> <span class="nu0">0</span><span class="sy4">;</span>
<span class="br0">}</span></pre></div></div>
<p>输出：
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="text source-text"><pre class="de1">current exceptions raised: none
current rounding method:   FE_TONEAREST
 
+11.5 -&gt; +12.0
+12.5 -&gt; +12.0
current exceptions raised: FE_INEXACT
current rounding method:   FE_TONEAREST
 
1.0/0.0 = inf
+11.5 -&gt; +11.0
+12.5 -&gt; +12.0
current exceptions raised: FE_DIVBYZERO FE_INEXACT
current rounding method:   FE_DOWNWARD
 
current exceptions raised: FE_INEXACT
current rounding method:   FE_TONEAREST</pre></div></div> 
</div>
<h3><span class="mw-headline" id=".E5.BC.95.E7.94.A8">引用</span></h3>
<div class="t-ref-std-11">
<ul><li> C11 standard (ISO/IEC 9899:2011): 
</li></ul>
<dl><dd><ul><li> 7.6.4.1 The fegetenv function (p: 213)
</li></ul>
</dd></dl>
<dl><dd><ul><li> 7.6.4.3 The fesetenv function (p: 214)
</li></ul>
</dd></dl>
<div class="t-ref-std-c99">
<ul><li> C99 standard (ISO/IEC 9899:1999): 
</li></ul>
<dl><dd><ul><li> 7.6.4.1 The fegetenv function (p: 194)
</li></ul>
</dd></dl>
<dl><dd><ul><li> 7.6.4.3 The fesetenv function (p: 195)
</li></ul>
</dd></dl>
</div>
<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">参阅</span></h3>
<table class="t-dsc-begin">

<tr class="t-dsc">
<td>  <div class="t-dsc-member-div"><div><a href="feholdexcept.html" title="c/numeric/fenv/feholdexcept"> <span class="t-lines"><span>feholdexcept</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-c99">(C99)</span></span></span></div></div>
</td>
<td>   保存当前环境的异常状态标志，再清除所有异常状态标志，并忽略所有未来错误 <br> <span class="t-mark">(函数)</span> </td></tr>

<tr class="t-dsc">
<td>  <div class="t-dsc-member-div"><div><a href="feupdateenv.html" title="c/numeric/fenv/feupdateenv"> <span class="t-lines"><span>feupdateenv</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-c99">(C99)</span></span></span></div></div>
</td>
<td>   恢复之前保存的浮点环境，并引发之前已经引发过的异常，使其存在于当前内存环境中 <br> <span class="t-mark">(函数)</span> </td></tr>

<tr class="t-dsc">
<td>  <div class="t-dsc-member-div"><div><a href="FE_DFL_ENV.html" title="c/numeric/fenv/FE DFL ENV"> <span class="t-lines"><span>FE_DFL_ENV</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-c99">(C99)</span></span></span></div></div>
</td>
<td>   默认浮点环境 <br> <span class="t-mark">(宏常量)</span> </td></tr>

</table></div>

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